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"I would leave a small amount of R in series with the gates for two reasons;

1. it helps dampen any tendency of the network and other strays to ring (Better drive waveforms).

2. should a transistor failure occur, it prevents the output of the driver from going complete short circuit. I have lost a few drivers due to transistor failure, No more once a little R was added. I'm using three 10 ohm 1206 resistor in parallel to make a wider low L resistor, and also spread the dissipation."

"I would leave a small amount of R in series with the gates for two reasons;

1. it helps dampen any tendency of the network and other strays to ring (Better drive waveforms).

2. should a transistor failure occur, it prevents the output of the driver from going complete short circuit. I have lost a few drivers due to transistor failure, No more once a little R was added. I'm using three 10 ohm 1206 resistor in parallel to make a wider low L resistor, and also spread the dissipation."

+-RH

Quite a few years ago I designed a dual 400 watt MOSFET PSU based switcher for x-ray tubes (final output was up to +/- 200 kV). I also found that a small resistance in series with the gate drive was good protection.

"I would leave a small amount of R in series with the gates for two reasons;

1. it helps dampen any tendency of the network and other strays to ring (Better drive waveforms).

2. should a transistor failure occur, it prevents the output of the driver from going complete short circuit. I have lost a few drivers due to transistor failure, No more once a little R was added. I'm using three 10 ohm 1206 resistor in parallel to make a wider low L resistor, and also spread the dissipation."

+-RH

Quite a few years ago I designed a dual 400 watt MOSFET PSU based switcher for x-ray tubes (final output was up to +/- 200 kV). I also found that a small resistance in series with the gate drive was good protection.

"I would leave a small amount of R in series with the gates for two reasons;

1. it helps dampen any tendency of the network and other strays to ring (Better drive waveforms).

2. should a transistor failure occur, it prevents the output of the driver from going complete short circuit. I have lost a few drivers due to transistor failure, No more once a little R was added. I'm using three 10 ohm 1206 resistor in parallel to make a wider low L resistor, and also spread the dissipation."

+-RH

Quite a few years ago I designed a dual 400 watt MOSFET PSU based switcher for x-ray tubes (final output was up to +/- 200 kV). I also found that a small resistance in series with the gate drive was good protection.

The frequency was a bit lower than 43 meters

X-ray tubes...I hear those things are dangerous!

I actually just re-found the videotape (yes, videotape, it's from 1994) of the CEO of the company I worked for at the time testing out the prototype. With a long lucite rod and a ground wire. Many arcs were made. Digitizing it for posterity.

Well, the non-inverted side already works fine (with less than 12V). After reading the truth table again, I don't see why this wouldn't work. Unfortunately, the only way to find out is to send for the PCBs again. I'm just going to go for it. It's only $35 for 6 of them and it's not something I can hack onto my current board because those pins are grounded, so I can't just connect a wire there; I have to get new PCBs. And I shouldn't need pullups or pulldowns because that pin should always be high.

Lift the grounded pin and wire high.

Put a sharp blade under the leg, heat and bend up. I wouldn't got to any extra expense until it's proven.

The whole amp is passively cooled and barely gets warm at carrier, so cool in fact I wonder where the power is coming from!

The whole system is calibrated so I know it accurate to a few %, DC and RF wise.

12V I is around 410mA and that's for 4 NCP's and the AD9850 (which gets a bit warm).

So I rekon around 80/90mA per driver?

The drivers do warm up but I can just keep my finger on them (for a while!)

I run the NCP's at 12V and noticed ONLY a 0.3% increase in eff moving to 15V, so 12V is fine.

So not sure why your having the heat problems.

Your layout isn't that different from mine except that I am trying to use the built-in inverted inputs.It's too hard and kludgy to try and lift those pins, so I just ordered a new board. Waiting for it to arrive now.

It could be because I put too much thermal paste under the fets and it bulged out and bridged the gate and source. It's not conductive and I've verified that, but it could be a little capacitive. That's my only guess. I'll be careful not to do that when I install the fets on the new board. They do seem to work alright at 10V, so that's what I am going to use. 12V and I can't put my finger on them for more than a second. I may be able to find a type of heatsink like they use on motherboard voltage regulators if I decide to run it at 12V.

Eff will suffer at 10V and FETs wont be fully on and dissipate more heat.

Don't know why you can't just whip off the drivers with a hot air gun, bend the pin and reseat or just lift the pin with a scalpel whilst heating with an iron. I'd always breadboard first.

However you should be ok with the design now. Don't use any grease and just use the greasless insulators (orange ones).

Str.

My PCB company is so fast that it's not worth the effort. The board arrived yesterday and I finished installing everything and tested it.The inverted inputs work!!!The efficiency (87%) is not too good, but I know the reason why and I think I can fix it.The way I connected my balun, I think is a little unbalanced I need 270pf on one side and nothing on the other to produce the 87%, so I've got a balance issue. I am going to fix the balun because with the way it connects, the one side is a little longer.That should help and then I am going to try 12V with some little heatsinks and see if I can get into the nineties.

At 12V 4 of my NCPs draw 430mA (operating at 10V through regulators), but that's along with the crystal oscillator and voltage regulators which get a little warm.

So I've done a bit more experimenting. I made it to 92% @ 6.8 MHz with 12V drive. Something is a little weird though. I need exactly 470pf on only one side of the amp. Like I said before, I think I need to change my balun back to the original wire wrapped one I was using. This new one uses coax and it's a bit strange. Could I somehow be fooling the bird meter by using a cap on one side only? If not, then it's got to be my balun. I'm going to put the old one back in tomorrow and see. The new one was actually 1% less efficient or in the noise.

I should never need more capacitance on one side, right? Each side of the amp is exactly the same, so I am guessing it has to be the balun.

Be careful using the '3180's as they have very limited drive capability. The datasheet only specs them to about 63 KHz for full current output, and I have smoked a few of them running larger fets, see page 10 of the ON/Fairchild datasheet. If you are using a half bridge type arrangement (totem pole) you can use a bootstrap type supply to derive VCC for the upper driver. This doesn't work very well on single ended (non push-pull) arrangement however.

I wound up using a HCPL7723 driving a TC4452 and this has been rock solid into anything I've tried. The only downside is the photocoupler requires 5V (on both sides, mind you), the driver closer to 12V for good modulator efficiency.